As a conventional noise filter, a technology disclosed in Non-Patent Document 1 is known. This conventional noise filter is configured with two coils, two across-the-line condensers (hereinafter, referred to as an X condenser); the two coils are connected between the respective one terminals and the respective other terminals of the two X condensers; this noise filter is configured in such a way that there is provided a path through which an electric current having a direction opposite to the direction of an electric current flowing in the one of the two X condensers flows in the other one. In the conventional noise filter configured in such a manner as described above, because when an electric current flows in the one X condenser, an opposite-direction electric current flows in another path; therefore, magnetic fluxes generated by the electric currents flowing the respective paths are cancelled each other, so that magnetic coupling with the other X condenser is suppressed. As a result, the normal-mode attenuation amount in the noise filter is substantially improved.
Patent Document 1 discloses, as a circuit technology that can be utilized in a filter, a method of suppressing magnetic coupling between condensers by the way in which the respective condensers are arranged. In this method, a plurality of condensers that are connected in parallel with one another are arranged in such a way that the vector of an electric current flowing in one of the plurality of condensers is not parallel to the vector of an electric current flowing in another (adjacent) condenser, so that magnetic coupling between the condensers is suppressed.